Not sure what his diet is, but I eat low carb during the week and have carbs on the weekend.

I eat when hungry and it works well, as long as I don't try to undereat fats.

It's actually fairly complex, but it's similiar to what you did when you tried IF. Most days you drink 5-6 protein shakes and eat 1 or 2 meals consisting almost entirely of fatty meat, prefferably bone-in. 1 or 2 days a weak you do a refeed or "rampage" with lots of carbs. You also do a "protein sparing fast" once a week which is a day of just protein shakes.

I've never been able to eat just when I'm hungry. That's why I can gain so much weight so easily, and why I lean towards more structured diet plans.